Typical materials requiring surface flatness at high level include a single-crystal silicon disk called a silicon wafer for producing semiconductor integrated circuits (IC, LSI). The surface of the silicon wafer should be flattened highly accurately in a process of producing IC. LSI etc., in order to provide reliable semiconductor connections for various coatings used in manufacturing the circuits. In the step of polishing finish, a polishing pad is generally stuck on a rotatable supporting disk called a platen, while a workpiece such as a semiconductor wafer is stuck on a polishing head. By movement of the two, a relative speed is generated between the platen and the polishing head while polishing slurry having abrasive grains is continuously supplied to the polishing pad, to effect polishing processing.
As polishing characteristics of a polishing pad, it is requested that a polished object is excellent in planarity and within wafer non-uniformity and a polishing rate is large. A planarity and within wafer non-uniformity of a polished object can be improved to some extent with a polishing layer higher in elastic modulus.
Considering the development of next-generation devices, there is a demand for high-harness polishing pads capable of further improving flatness. In order to improve flatness, non-foamed hard polishing pads may also be used. When such hard pads are used, however, a problem can occur in which material surfaces are scratched when polished. Also in view of polishing rate, non-foamed polishing pads are not preferred, because their surfaces cannot hold a sufficient amount of abrasive grains from a slurry during polishing. As the hardness of polishing pads increases, their wear resistance tends to decrease. Therefore, high-hardness polishing pads may have a problem with respect to a demand for life elongation.
Also proposed is a polishing pad including a water-insoluble thermoplastic polymer and a water-soluble material dispersed therein (see Patent Literature 1). Although this polishing pad is a non-foamed product, the water-soluble material dispersed in the polishing pad dissolves during polishing so that pores like a foam are formed in the surface of the polishing pad, and that the polishing pad is allowed to swell and thus has reduced surface hardness, which is effective in reducing scratches and improving the polishing rate. However, since the surface of this polishing pad is allowed to swell and thus has reduced hardness, its planarization performance is insufficient.
In order to achieve both an improvement in planarity and a reduction in scratches, a polishing pad is disclosed which include a polymer of an isocyanate-terminated prepolymer produced by a reaction of an organic polyisocyanate, a high molecular weight polyol containing a water-soluble polymeric polyol, and a low molecular weight polyol, and a chain extender (see Patent Literature 2). However, since the surface of this polishing pad is also allowed to swell and thus has reduced hardness, it cannot offer satisfactory planarization performance that will be required in the future.
Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2001-47355
Patent Literature 2: Japanese Patent No. 3571334